Prepare docstrings for doc generation from docstrings

Also fix ridiculous indentation.

* api.lisp (uri-to-arguments, arguments-to-uri)
(read-for-resource, write-for-resource, handle-request)
(documentation, backend-payload): Fix docstrings.

* common.lisp (find-content-class, verb-spec-or-lose)
(parse-resource, parse-content-type-header, check-optional-args)
(genpath-fn-lambda-list, explain-failsafe): Fix indentation.
(arguments-to-uri-1, uri-to-arguments-1, read-for-resource-1)
(write-for-resource-1): Rename from ARGUMENTS-TO-URI,
URI-TO-ARGUMENTS, READ-FOR-RESOURCE and WRITE-FOR-RESOURCE,
respectively.